The invention relates to processing block coded image data. The Consultative Committee for International Telephony and Telegraph (CCITT) has adopted a standard (H.261) for encoding image data representative of a sequence of two dimensional arrays of image data. According to the proposed standard, a two dimensional array of pixel data is divided into a plurality of blocks, each block including an 8.times.8 sub-array. Each block of data is encoded using a lossy encoding technique to reduce the number of bits required to represent the block. The encoded data is then transmitted to a remote device which reconstructs the entire image from the transmitted data.
The image reconstructed from the encoded blocks does not perfectly correspond to the original image. In each block of data, image information is lost when the data is compressed to reduce the number of bits for transmission. Since each block is separately coded, the losses in one block differ from those of adjacent blocks. As a result, a noticeable line appears at the boundaries between the blocks.
One object of the invention is to process the pixels near the boundaries between adjacent blocks to reduce or eliminate the noticeable boundary caused by block encoding. Another object of the invention is to efficiently examine the pixel data near the borders between blocks to determine if the image includes edges in the vicinity of the border. If such edges are detected, the pixels near the border are processed to reduce the coding artifacts caused by block encoding without removing or distorting edges which appear in the image.